Rolled tissue product

ABSTRACT

Provided are rolled tissue products, particularly rolled towel products, configured for peripheral dispensing having improved dispensing and consumer satisfaction. The products comprises a plurality of sheets spirally wound around a core where individual sheets are separated from one another by a line of perforations divided into multiple zones where each of the zones has a different bonded area. The different zones have different detach strength because of the difference in bonded area. Compared to products having a line of perforations with a single strength or bonded area across the entirety of the perforation line length, the products have comparable or better detach strength but are less susceptible to dispensing failures.

BACKGROUND

Rolled tissue products typically comprise a web of individual sheets, where the sheets are separated from one another by a line of perforations in order to facilitate the tearing off of the desired sheets from the web in a neat and undamaged fashion. The perforations are normally provided in transverse perforation lines across the width of the web and may be uniformly spaced in the machine direction of the roll to provide individual sheets of uniform length. Typically a line of perforations comprise alternating bonded areas and cuts.

Perforating devices are well known in the art of tissue product manufacturing and are incorporated into almost all bathroom tissue and towel winders as well as other converting equipment in a typical tissue manufacturing process. These devices comprise a perforator roll, which holds a plurality of perforator blades, and an anvil head, which holds a plurality of anvil members. Each individual perforator blade may extend across the width of the perforator roll and be spaced circumferentially and axially in an operative. The blades may be arranged in a generally helical path along the outer periphery of the perforator roll as to keep all of the perforator blades from striking the anvil at the same time, thus minimizing the amount of vibration at the point of perforation. The perforator blades are typically specified by the length of the bonds (distance between adjacent teeth for cutting the web) and the number of bonds for a given blade length. Both the number of bonds and the length of the bonds must be balanced to provide a product having perforation lines with sufficient bond strength to operate efficiently and without breaks on the converting equipment, and yet weak enough to provide easy and undamaged sheet separation by the consumer. This balance is difficult strike however, and the tissue maker is constantly trying to optimize perforations to improve both runnability and dispensing.

Poor detaching usually manifests itself to the consumer as the incomplete removal of a sheet of tissue at the line of perforations. Usually the web will start to tear at the perforation line, but as the tare progresses across the line of perforation in the roll width, the web will start to tear longitudinally in the machine direction rather than transversely across the roll at the perforations. The result is typically the leaving of a piece of sheet that had been detached at the far end of the roll from which the detaching had been initiated. Another fairly common problem is that the bond strength is too high, favoring good operation of the converting equipment, but when the sheet is detached, the web initially tears in some spot other than at the line of perforation. This is particularly common in single-ply tissue products because of localized variations in formation and basis weight which cause weaknesses in the sheet that lead to a tearing at a location other than the perforation.

Hence there is a need to provide a perforated product that detaches more uniformly and completely at the perforations such that the detached sheet is in its whole undamaged form after detaching. There is also a need to maintain good operational efficiency of the converting equipment without failure of the web caused by perforations bonds being too weak.

SUMMARY

It has now been surprisingly discovered that a balance between machine runability and dispensing may be struck by providing roll tissue product with lines or perforations having multiple zones where each of the zones has a different bonded area. Particularly, it has been discovered this balance is best struck when the line of perforations comprises five or more zones where the percent bonded area differs amongst at least three of the zones. In this manner a single line of perforations may have a first zone with a first percent bonded area, a second zone with a second bonded area and third zone with a third bonded area where the percent bonded area increases from the first to the second zone and then from the second to the third zone. As a result of the difference in the percent bonded area the relative detach strength of the zones also differs, with the highest detach strength found in the zone having the highest percent bonded area.

Preferably the zone having the lowest bonded area, or lowest detach strength, is disposed adjacent to the sheet edge. The bonded area may then be increased for the next adjacent zone and yet again for the next adjacent zone such that the bonded area increases from the first edge of the tissue sheet to a central portion of the tissue sheet. The bonded area may then decrease from the central portion to the opposite tissue edge. In certain instances the increase in the bonded area from the first zone (nearest sheet edge) to a third zone (nearest the sheet mid-point) may be linear.

The difference in percent bonded length between the edges and the central portion of the web need not be large on an absolute basis. Absolute percent boned length differences can be about 2% or greater, more specifically from about 2% to about 25%, more specifically from about 2% to about 10%, and still more specifically from about 2% to about 5%. In any given instance, the difference in percent bonded length will largely depend upon the overall strength of the tissue sheet and the percent bonded area in the central portion of the sheet. For a towel product having a geometric mean tensile strength of about 2,000 g/3″ or more, for example, the percent bonded area in the central portion of the towel typically ranges from about 18% to about 28%, such as from about 20% to about 28%, such as from about 22% to about 28%.

Accordingly, in one embodiment the present invention provides a tissue product comprising a tissue web spirally wound about a core and configured for peripheral dispensing, the tissue web comprising a plurality of spaced apart transverse lines of peroration that define individual tissue sheets therebetween, each sheet having a sheet length (l), a sheet width (w), a first edge, a second edge and a midpoint disposed equal distance between the first and second edges, wherein the line of perforations comprise a first zone beginning at a the first edge and having a first bonded area, a second zone disposed adjacent to the first zone and having a second bonded area and a third zone disposed about the midpoint and having a third bonded area and wherein the first bonded area is less than the second bonded area, which is less than the third bonded area.

In another embodiment the present invention provides a tissue product comprising a tissue web spirally wound about a core and configured for peripheral dispensing, the tissue web comprising a plurality of spaced apart transverse lines of peroration that define individual tissue sheets therebetween, each sheet having a sheet length (l) and sheet width (w), each of the lines of perforations further comprising varying bonded areas that define opposite edge zones, opposite intermediate zones and a middle zone, wherein the bonded area of the opposite edge zones is less than the bonded area of the opposite intermediate zones and the bonded area of the opposite intermediate zones is less than the bonded area of the middle zone.

In still another embodiment the present invention provides a rolled tissue product comprising a tissue web spirally wound about a core and configured for peripheral dispensing, the tissue web comprising a plurality of spaced apart transverse lines of peroration that define individual tissue sheets therebetween, each sheet having a sheet length (l) and sheet width (w), each of the lines of perforations further comprising varying bonded areas that define opposite edge zones having a bonded area from about 20% to about 21%, opposite intermediate zones having a bonded area from about 22% to about 23% and a middle zone having a bonded area from about 24% to about 25%.

In yet another embodiment the present invention provides a method of manufacturing a rolled web of paper material comprising differentially perforating the web with a plurality of spaced-apart perforation blades to provide spaced-apart lines of perforations extending transversely across the web, the lines of perforations further comprising varying bonded areas that define opposite edge zones, opposite intermediate zones and a middle zone, wherein the bonded area of the opposite edge zones is less than the bonded area of the opposite intermediate zones and the bonded area of the opposite intermediate zones is less than the bonded area of the middle zone.

Other features and aspects of the present invention are discussed in greater detail below.

DESCRIPTION OF THE DRAWINGS

Various non-limiting embodiments are further described with reference to the accompanying drawings in which:

FIG. 1 illustrates a roll or tissue product configured for peripheral dispensing;

FIG. 2 illustrates a line of perforations having five zones;

FIGS. 3A and 3B illustrate a perforation blade and detail portion thereof;

FIG. 4 is graph of a theoretical detach strength having units of grams force (gf) versus sheet width having units of inches for a five zone perforation pattern according to one embodiment of the invention; and

FIG. 5 is graph of a tissue product detach strength having units of grams force (gf) versus various dispensing properties for tissue products prepared as described in the Examples section, codes 1-6 (●), inventive code 7 (Δ) and code 8 (□).

DEFINITIONS

As used herein, the term “machine direction” (MD) generally refers the direction in which a tissue web or product is manufactured or converted. The term “cross-machine direction” (CD) means the direction that is substantially perpendicular to the MD.

As used herein the term “tissue web” refers to a fibrous sheet suitable for forming a tissue product. The tissue web may be formed by any one of the papermaking processes described herein. In certain instances, a tissue web comprises fibrous sheet that has not been subjected to further processing, such as embossing, calendering, perforating, plying, folding, or spiral winding about a core, to convert the sheet into a finished tissue product.

As used herein the term “tissue product” refers to a finished product salable to a consumer made from a tissue web. Non-limiting examples of tissue products include bath tissue, facial tissue, paper towels, industrial wipers, foodservice wipers, napkins, and medical pads. Tissue products may comprise one, two, three or more plies and may have a basis weight from about 10 to about 100 grams per square meter (gsm) and a sheet bulk greater than about 3 cubic centimeters per gram (cc/g), such as from about 3 to about 20 cc/g and more preferably from about 10 to about 15 cc/g.

As used herein, the term “separably joined” generally refers to adjacent sheets within a continuous web that may be separated from one another along a line of weakness.

As used herein, the term “line of perforations” generally refers to a portion of a web or product that is more readily ruptured, or torn, upon application of a tearing force to the web or product. The line of perforations may be suitably formed by mechanical cutting, pressure cutting, ultrasonic cutting, thermal deformation, mechanical thinning, or other suitable techniques. As an example, with reference to FIG. 1 , the line of perforations 10 may comprise a plurality of cuts 16 separated from one another by bonds 17 and extending in the CD from a first edge 18 to second edge 19 of the sheet 5. A line of perforations may be linear or non-linear in shape. Non-linear shapes can include curved or arcuate profiles, a saw tooth profile, a zigzag profile, a sinusoidal profile, or any other geometrical profile that is not a straight line.

As used herein, the term “perforation” generally refers to one or more holes, slits, apertures, voids, or the like, or combinations thereof through a fibrous structure to facilitate separation of one portion of the structure from another. For example, a perforation may be a portion of a tissue web that has been mechanically severed. Perforations may be disposed on a tissue web to provide sheets that are separably joined. In certain embodiments the perforations may comprise a linear set of apertures generally extending in one dimension of the web, such as the CD, which may be described as a line of perforations. In other embodiments the line of perforations may be non-linear.

As used herein, the terms “bond length” refers to the length of a nonperforated segment of the web in the line of perforations. Said another way, it is the distance between adjacent perforations. Perforations that are useful with sheets of the invention may have a bond length in the range from about 0.40 mm to about 1.0 mm, such as from about 0.50 mm to about 0.90 mm. The foregoing are non-limiting and the as the perforation configuration is dependent upon many factors including base sheet characteristics (e.g., fiber composition, formation process, bulk, density, thickness, weight, CD tensile, MD tensile), operating conditions, such as log winding speeds and tensions, and others that can affect how one sheet separates from another sheet and/or dispenses from a dispenser.

As used herein, the term “percent bonded area” when referring to a line of perforations or a zone within a line of perforations is equal to:

$\frac{{Number}{of}{Bonds}x{Bond}{Length}({mm})}{{Zone}{or}{Sheet}{Width}({mm})}$

When referring to a perforation blade useful in the present invention “percent bonded area” for a given length of blade is equal to the number of recesses within the given length multiplied by the recess width, divided by the given blade length.

Lines of perforations useful in the present invention generally have zones with different percent bonded area. For example, a line of perforations may comprise first, second and third zones, where the first zone has a percent bonded area of about 15% to about 22%, the second zone has a percent bonded area of about 20% to about 25% and the third zone has percent bonded area of about 22% to about 28%. In certain preferred embodiments the percent bonded area of the first zone is less than the percent bonded area of the second zone, and the percent bonded area of the second zone is less than the percent bonded area of the third zone.

As used herein, the term “detach strength” refers to the force in grams (g) per sheet that is required to break the line of weakness. In one non-limiting example the detach strength may be the force in grams (g) per sheet that is required to separate two sheets in a tissue web spirally wound into a roll along a line of perforations. Detach strength is measured as described in the Test Methods section below. The detach strength for a given tissue product may vary depending on the fiber composition, formation process, bulk, density, thickness, weight, CD tensile, MD tensile of the product, however, in certain embodiments the detach strength may range from about 1300 gf to about 3000 gf, such as from about 1500 gf to about 2800 gf.

As used herein, the term “theoretical detach strength” refers to the theoretical force in grams (g) that is required to break a line of weakness within a given zone. Because a zone is a discrete portion of a line of perforations the detach strength of the zone may not be amendable to conventional measurement of detach strength as described herein. Instead, the detach strength of the zone may the theocratized by manufacturing a substantially similar tissue product having a line of perforations with a percent bonded area equal to the percent bonded area of the given zone and measuring the detach strength of the tissue product.

DETAILED DESCRIPTION

The present invention generally relates to rolled tissue products comprising a spirally wound web of tissue configured for peripheral dispensing of individual tissue sheets. The rolled tissue may comprise a core, typically made of stronger material than the tissue (for example cardboard) that is centrally located and around which the web of tissue is wound. Typically rolled tissue products comprise a central void space, which space may be defined by the core.

The tissue web is a substantially flat and flexible sheet and may include cellulosic sheets such as those conventionally used in paper towels, bath tissue, wipers, or the like. Tissue webs useful in the present invention may comprise a single ply or may comprise multiple plies assembled together to obtain a multi-ply tissue product. The plies can be joined by embossing, glue, or any other suitable means. Typically tissue webs suitable for the present invention are manufactured by a conventional wet-laying of fibers such as conventional paper-making or through-air dried paper-making.

Regardless of the process by which it is made, tissue webs and products of the present invention will generally have different physical properties, such as tensile strength, in the machine and cross-machine direction. In one embodiment the present invention comprises a rolled paper towel product configured for peripheral dispensing, the paper towel product having a tensile ratio of about 2.0 or less, such as from about 1.0 to about 2.0 and a GMT of about 1500 g/3″ or more, such as from about 1500 g/3″ to about 2500 g/3″, such as from about 2000 g/3″ to about 2400 g/3″. The CD tensile of the foregoing products may range from about from about 1800 g/3″ to about 2500 g/3″, such as from about 2000 g/3″ to about 2500 g/3″.

The webs of the present invention, which have repeating lines of weakness, are preferably manufactured such that lines of weakness are sufficiently strong to maintain the integrity of the web during converting, but weak enough to separate a selected sheet from the remainder of the rolled product in use. Accordingly, the products of the present invention may have a detach strength of at least about 1000 gf, such as at least about 1500 gf, such as at least about 1800 gf, such as at least about 2000 gf, such as from about 1000 gf to about 3000 gf. In certain preferred embodiments the tissue products, particularly rolled paper towel products having a GMT of about 1500 g/3″ or more, such as from about 1500 g/3″ to about 2500 g/3″ and have a detach strength of at least about 1300 gf, such as at least about 1500 gf, such as at least about 1800 gf, such as at least about 2000 gf, such as from about 1500 gf to about 3000 gf, such as from about 2000 gf to about 3000 gf, such as from about 2500 gf to about 3000 gf.

In certain instances, the detach strength may be normalized based on the CD tensile of the products, that is grams (g) force per sheet divided by the CD tensile having units of grams per 76.2 mm to determine the “normalized detach strength.” Webs useful in the present invention may be rolled paper towel products having a CD tensile strength from about 1800 g/3″ to about 2500 g/3″, such as from about 2000 g/3″ to about 2500 g/3″, such as from about 2200 g/3″ to about 2500 g/3″ and a normalized detach strength of about 1.5 or less, such as from about 1.0 to about 1.5, such as from about 1.0 to about 1.25.

The rolled tissue products of the present invention may be produced using conventional converting processes such as unwinding a web, perforating the web, and then winding the perforated web along its length, that is, its greatest dimension to form a rolled tissue product. This dimension may also define the machine direction of the tissue web and the resulting rolled tissue product. The width of the tissue web is perpendicular to the length and typical also represents the height or width of the tissue roll, depending on how it is orientated in-use for dispensing. The width dimension may also define the cross-machine direction of the tissue web and the resulting rolled tissue product.

The tissue web may be divided into individual tissue sheets by multiple lines of perforations that delimitate the individual sheets and may facilitate separation of adjacent sheets from one another and dispensing of an individual sheet from the rolled tissue product. Preferably the lines of perforations create weaknesses in the tissue web that facilitate the detachment of the sheets. Typically, the lines of perforations are substantially transverse to the length of the tissue web. The line of perforations extend typically across the entirety of the width of the tissue web in order to better ease the detachment of the sheets. As will be discussed in more detail below, the relative strength of a given line of perforations may vary within the given line of perforations such that the given line of perforations has at least three different strengths.

The lines of perforations comprise slits, also referred to herein as perforations, and connecting regions, also referred to herein as bonded areas, of the tissue web. The slits are discontinuity in the tissue web, for example cuts where the web material is essential interrupted. The connecting regions generally span adjacent slits. The connecting regions have a length defined by the smallest distance between the two adjacent slits. The slits have a length that is defined by the maximum dimension of the discontinuity in the tissue web.

With reference now to FIG. 1 , a rolled tissue product 1 comprising a tissue web 5 spirally wound around a core 4. The core can be made of cardboard or any substantially robust material and can be cylindrical. The core can have a central void space enabling an element of a dispenser to serve as a central axis for the dispensing of the tissue web. Tissue rolls having a core present the advantage of making the roll less sensitive to damages and crushing. Also, the presence of a core facilitates the rotation of the tissue roll during dispensing. In one embodiment the dimension of the core correspond to the width of the rolled tissue product.

Preferably the tissue roll of the invention is a tissue roll for peripheral dispensing. Rolls for peripheral dispensing are particularly made and configured for that use. The roll illustrated in FIG. 1 is configured for peripheral dispensing. The sheets located at the periphery of the roll are accessible to the user and the first peripheral sheet is the first sheet dispensed by the user. Upon removal of the first peripheral sheet the next sheet becomes accessible to the user.

With continued reference to FIG. 1 , the tissue web 5 is illustrated as being unwound in the direction of the arrow. A detached elongated portion of tissue web 5 has a pre-determined length “L” as measured between two ends 12 and 14. The elongated tissue web 5 can be used “as is”, or it can be subdivided into individual sheets 6, 7, 8 and 9 by the consumer if desired. The four “sheets” 6, 7, 8 and 9 are separated from one another by lines of perforations 10, 10′ and 10″. The lines of perforations 10, 10′ and 10″ each comprise cuts or perforations 16 and bonds 17 resulting from mechanical severing of the web 5 during converting. The lines of perforations 10, 10′ and 10″ define individual sheets 6, 7, 8, and 9, which are separably joined. The line of perforations create a region of reduced strength which encourages the tearing off and separation of individual sheets of a predetermined size. The initiation of the detachment of the tear, in use, is most of the time at the first or second sheet edge. The lines of perforations 10, 10′ and 10″ are spaced apart from another in the machine direction (MD) and are generally linear and extend from a lateral first edge 18 to a lateral second edge 19 across the cross machine direction (CD).

The tissue roll of the invention comprises multiple lines of perforations. The lines of perforations are generally transverse to sheets length dimension and can be across the entirety of the sheet width. Preferably the line of perforations entirely across the width of the sheet such that a slit is within at least about 0.5 mm of the sheet edge. Deposition of a slit near the sheet edge may facilitate separation of individual sheets and reduce the occurrence of dispensing failures. A dispensing failure generally occurs when the sheet to dispense does not tear along the line of perforations, but rather tears at an angle relative to the line of perforations. Such tears generally reduce the useful area of the sheet and may make it unusable for the user.

The lines of perforations of the invention have a general shape that is associated to the disposition of the corresponding perforations and bonded areas. A line of perforation of the invention may have any number of different shapes, such as a straight line, a multiplicity of line segments, for example having a V-shape or a W-shape, or a curved line. In one embodiment of the line of perforations extends in a substantially straight line from a first tissue edge to a second tissue edge and is arranged substantially parallel to the cross-machine direction of the sheet.

Within a given rolled product the lines of perforations may all have the same shape, or the shape may differ. Regardless of the shape, the lines of perforations delimitate individual sheets and create weaknesses between sheets for easing the detachment of the sheets upon dispensing. Typically, the user pulls one corner of the sheet, beginning at first sheet edge, and the line of perforations induces the sheet to detach along the line. This is beneficial for obtaining a clean detachment of the sheet without undesired tearing of material.

To facilitate ease of tearing along the line of perforations and reduce the instances of undesired tearing, the rolled products of the present invention are provided with lines of perforations with variable degrees of bonded area across their width. In particularly preferred instances a line of perforations comprises at least three zones where each zone has a different bonded area. For example, with reference now to FIG. 2 , one embodiment of a line of perforations 10 comprising first through fifth zones 21, 22, 23, 24, 25 comprised of cuts or perforations 16 and bonds 17. Each of the first through fifth zones 21, 22, 23, 24, 25 has a length measured along the width of the web 5. The percent bonded area within a given zone varies between the first, second and third zones. For example, in the illustrated embodiment the first zone 21 may have a bonded area of about 20%, the second zone 22 may have a bonded area of about 22% and the third zone 23 may have a bonded area of about 24%. Further, the bonded area of the first and fifth zones 21, 25 may be substantially equal and the bonded area of the second and fourth zones 22, 24 may be substantially equal.

The number of zones within a given line of perforations may range from about 5 to about 11, such as from about 5 to about 7. In a particularly preferred embodiment, such as the embodiment illustrated in FIG. 2 , a line of perforations 10 has five zones 21-25. The first and fifth zones (edge zones) 21, 25 are adjacent to the first and second tissue sheet edges 18, 19 have a first bonded area and first theoretical detach strength. The second and fourth zones (intermediate zones) 22, 24, lie between the first and third zone 21, 25 and have a second bonded area and second theoretical detach strength. The third zone 24 (middle zone), has a third bonded area and a third theoretical detach strength. Preferably the first bonded area is less than the second bonded area, which is less than the third bonded area. In this manner the line of perforations has at least three different theoretical detach strengths along its width—beginning with a relatively low strength at the first edge, transitioning to a slightly higher strength in the intermediate zone, and then a still high strength in the middle zone.

Without being bound by the theory it is believed that providing multiple strength zones along a single line of perforations—from weak to strong and then back to weak—solves technical advantage during manufacturing while improving dispensing. The inventive tissue products have lines of perforations which balance the resistance to tearing during the manufacturing—generally forces parallel to the web length—and dispensing by a user—forces that are perpendicular to the web length. This allows for a more convenient dispensing of the sheet upon use without sacrificing process-ability of the web.

In certain instances, the change in detach strength between the first zone, that is the zone nearest the tissue edge, and the middle zone, that is the zone having highest theoretical detach strength and located approximately about the midpoint of the tissue sheet width, may be substantially linear. For example, for a tissue sheet having a GMT of about 2,200 g/3″, the first zone may have a theoretical detach strength of about 2100 gf, the intermediate zone may have a detach strength of about 2300 gf and the middle zone may have a detach strength of about 2500 gf.

In other instances, the first zone may have a theoretical detach strength of about 2200 gf or less, the intermediate zone may have a theoretical detach strength from about from 2200 to about 2400 gf and the middle zone may have a theoretical detach strength of about 2500 gf. In this manner the change in theoretical detach strength between zones is not overly abrupt and prevents tearing of the web and dispensing failures. In certain preferred embodiments the increase in the detach strength from the first zone to the middle zone is substantially linear.

In other instances, the length of each of the zones may be substantially identical and in other instances the relative length of the zones may differ. For example, the length of the first and fifth zones may be different than the length of the second and fourth zones, which may be different than the length of the third zone. In the embodiment illustrated in FIG. 2 , the weakest zones in terms of theoretical detach strength, the first and fifth zones 21, 25, are disposed adjacent to the respective sheet edges 18, 19 and comprise about 30% of the length of the perforation line 10. The intermediate zones 22, 24 comprise about 40% of length of the perforation line 10 and the middle zone 23 comprises about 30%. This foregoing percentages for each of the zones is merely one suitable embodiment and is not intended as a limitation of the invention.

The bonded area may be controlled by increase or decreasing the length of the perforations which, as described in more detail below, are imparted by the teeth of a perforating blade during converting. The perforations may have a length from 0.5 mm and 4.0 mm, such as from about 1.5 mm to about 3.5 mm, such as from about 2.5 mm to about 3.5 mm. In other instances, the length of the bonded area (i.e., the bond length) may be increased or decreased and may range from about 0.4 mm to about 1.0 mm, such as from about 0.50 mm to about 0.90 mm.

The length of the zones—the edge zones, intermediate zones, and middle zone—will depend on the profile of the individual perforation blades, as well as the blade pattern across the entire perforation line. For example, as explained in greater detail below, a perforation blade particularly useful in the present invention has a length approximately equal to the width of the rolled product and is divided into five distinct perforation zones of substantially equal length. The blade may have a weak/strong/strongest/strong/weak profile where detach strength of a given zone is varied by adjusting the length of the perforations. In this manner the perforation length is greatest in the weak zone and decreases for the strong and strongest zones. Alternatively, the blade may have perforations of substantially equal length, but the length of the bonded area may be varied between the zones to achieve the desired theoretical detach strength for each of the zones.

When converting a parent roll of tissue into individual rolled and perforated products of the present invention multiple perforation blades ay be aligned end to end or single perforation blade may be used. Regardless of the number of blades used to carryout perforation, the perforation blade 40 has a blade length (BL) and a first edge portion 41 comprising a plurality of teeth 45 and recesses 50. The recesses 50, have a recess width 51, which ultimately correspond to the bond length in the perforated tissue product, and a recess depth 53. Each tooth 45 is bordered by two opposing side walls 47. For example, tooth 45A includes side walls 47A and 47B. Two side walls from adjacent teeth form a recess. The recesses form bonds into the sheet material that separate the perforations along the perforation line. The teeth form a corresponding perforation into the web during the perforation process. Consequently, perforations formed in the web also have a width along a perforation line that substantially corresponds to the width 49 of the tooth 45.

The size, spacing and arrangement of the recesses and teeth may be configured to form an edge 41 having at least five zones 42 a, 42 b, 44 a, 44 b and 46 where the bonded area of first zones 42 a, 42 b is different than that of second zones 44 a, 44 b, which differs still from that of the third zone 46. In the illustrated embodiment the first zones 42 a, 42 b are disposed nearest the blade first and second ends 57, 59 have a relatively low bonded area compared to the second zone 44 a, 44 b and third zone 46. The bonded area of the second zone 44 a, 44 b is higher than the first zone 42 a, 44 b, but lower than the third zone 46.

In the embodiment illustrated in FIG. 3A, the recesses 50 of the first zones 42 a, 42 b have a width of about 3.45 mm and are arranged to provide a bonded area of about 20.5%. The recesses 50 in the second zones 44 a, 44 b may range from about 0.5 mm to about 1.0 mm and are arranged to provide a bonded area of about 21.9%. Finally, the recesses 50 in the middle portion 46 may range from about 0.5 mm to about 1.0 mm and are arranged to provide bonded area of about 23.3%.

The size, spacing and arrangement of the teeth and recesses of the embodiments illustrated in FIGS. 3A and 3B are merely illustrative and are not intended to limit the scope of the present invention. In certain embodiments the teeth, and the resulting perforations, may have a length from about 0.5 mm and 4.0 mm, such as from about 1.5 mm to about 3.5 mm. The recess, and the resulting bonded areas, bonds may range from about 0.5 mm to about 1.0 mm. In certain embodiments it may be desirable for both the bond length and perforation lengths to be uniform within a given zone, while in other embodiments the lengths of the bonds and perforations may vary within a zone or between zones.

The perforation blades of the present invention may be paired with an anvil roll comprising a plurality of anvils to perforate a tissue web using well known perforation processes. For example, a web may be conveyed between the perforation blade- and the anvil roll. As the web passes between the blade and the anvil roll, the anvils strikes the perforation blade and forms a perforation line into the web. The spacing of the anvils on the anvil rot and the speed at which the anvil rot rotates relative to the sheet material as it is conveyed determines the distance between transverse perforation lines.

In one embodiment, the anvils include an incline surface that contacts the teeth of the perforation blade. As the anvil contacts the perforation blade, the impact force between the teeth and the anvil increases until the anvil passes by the perforation blade. As the anvil moves past the perforation blade, an edge on the teeth forms perforations into the sheet material. During this process, the perforation blade strikes the moving anvil and is deflected as the anvil rotates beyond the blade. The rot blade is typically mounted at a 45 degree angle relative to the rot surface, while the stationary blade is mounted with a slightly greater angle of approximately 60 degrees.

Test Methods Detach Strength

Detach strength was measured using an MTS Systems Sintech 11 S, Serial No. 6233. The data acquisition software was an MIS TestWorks® for Windows Ver. 3.10 (MIS Systems Corp., Research Triangle Park, NC), For each measurement, two sheets were removed from a rot. The two sheets were separably joined by a line of perforations. The sheets were folded accordion style (7-pattern) and then the top and bottom of the sample along substantially the entire width were placed in grips having an internal spacing of 2 inches (50.8 mm), such that the perforation line was centered between the upper and lower grips. The upper grip was then displaced upward (i.e., away from the lower grip) at a rate of 10 inches/minute (254.0 mm/min) until the sample was broken along the perforations. The applied force and sample elongation were measured throughout the test. The peak load from the force-elongation curve is recorded so that the detach strength is expressed as force in units of grams/sheet. The average results from ten samples are reported as the detach strength having units of grams (g),

Tensile Strength

Tensile testing is conducted on a tensile testing machine maintaining a constant rate of elongation and the width of each specimen tested is 3 inches. Testing is conducted under TAPPI conditions. Prior to testing samples are conditioned under TAPPI conditions (23±1″C and 50±2% relative humidity) for at least 4 hours and then cutting a 3±0.05 inches (76.2±1.3 mm) wide strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (Thwing-Albert Instrument Company, Philadelphia, PA, Model No. JDC 3-10, Serial No. 37333) or equivalent. The instrument used for measuring tensile strengths was an MTS Systems Sintech 11S, Serial No. 6233. The data acquisition software was MTS TestWorks® for Windows Ver. 3.10 (MTS Systems Corp., Research Triangle Park, NC). The load cell was selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, such that the majority of peak load values fall between 10 to 90 percent of the load cell's full-scale value. The gauge length between jaws was 4±0.04 inches (101.6±1 mm) for facial tissue and towels and 2±0.02 inches (50.8±0.5 mm) for bath tissue. The crosshead speed was 10±0.4 inches/min (254±1 mm/min), and the break sensitivity was set at 65%. The sample was placed in the jaws of the instrument, centered both vertically and horizontally. The test was then started and ended when the specimen broke. The peak load was recorded as either the “MD tensile strength” or the “CD tensile strength” of the specimen depending on direction of the sample being tested. Ten representative specimens were tested for each product or sheet and the arithmetic average of all individual specimen tests was recorded as the appropriate MD or CD tensile strength having units of grams per three inches (g/3″). Tensile energy absorbed (TEA) and slope are also calculated by the tensile tester. TEA is reported in units of g·cm/cm² and slope is recorded in units of kilograms (kg). Both TEA and Slope are directionally dependent and thus MD and CD directions are measured independently.

All products were tested in their product forms without separating into individual plies. For example, a 2-ply product was tested as two plies and recorded as such. In the tensile properties of basesheets were measured, the number of plies used varied depending on the intended end use. For example, if the basesheet was intended to be used for 2-ply product, two plies of basesheet were combined and tested.

Example

A single ply uncreped through-air dried tissue web having a basis weight of about 33.4 gsm, a CD tensile of about 2300 g/3″ and a GMT of about 2300 g/3″ was converted into rolled products configured for peripheral dispensing by unwinding, perforating and spirally winding about a core. The web was converted into several different products using different perforation blades as set forth in Table 1, below.

TABLE 1 Perforation Code Zones Length (mm) % Bond Area 1 1 0.66 22.0% 2 1 0.66 18.5% 3 1 0.71 27.7% 4 1 0.71 30.8% 5 1 0.71 15.4% 6 1 0.46 12.9% 7 5 0.71 20.5%, 21.9%, 23.3%, 21.9% 20.5% 8 3 0.71 19.5%, 24.3%, 19.5%

The perforation blades (including the inventive and control blades) all had the same common characteristics with regards to the bond length (0.70 mm). The detach strength of samples 1-6 was measured and compared to the estimated detach strength, the results of which are summarized in Table 2, below.

TABLE 2 Estimated Detach Actual Detach Code Strength (gf) Strength (gf) 1 2250 2478 2 1800 2242 3 3150 2685 4 3600 3275 5 1350 1621 6 1350 1356

The inventive products (code 7) were produced using a perforation blade having five zones. The five zones had bonded areas of 20.5%, 21.9%, 23.3%, 21.9% and 20.5%. The weakest zones were disposed nearest the sheet edges and the strongest was disposed near the sheet midpoint. The theoretical detach strengths of each of the zones is plotted in FIG. 4 .

All of the codes were placed in a user handling study in which users were asked to peripheral dispense individual sheets from the rolled product. Incidents of tears during dispensing were recorded as was the overall user satisfaction with dispensing. The results are shown in FIG. 5 . FIG. 5 also shows that at lower detach strengths, such as less than about 2000 gf, users found dispensing to be relatively satisfactory with a low rate of dispensing failures (breaks or tears at sheet locations other than the line of perforations). On the other hand, products having a detach strength greater than about 2500 gf had lower satisfaction in dispensing and an increased rate of tearing at a location other than the perforation. The inventive products (code 7) provided dispensing satisfaction similar to that of control codes having lower detach strengths, even though the overall detach strength of the inventive products was higher. 

We claim:
 1. A rolled tissue product comprising a tissue web spirally wound about a core and configured for peripheral dispensing, the tissue web comprising a plurality of spaced apart transverse lines of peroration that define individual tissue sheets therebetween, each sheet having a sheet length (l) and sheet width (w), each of the lines of perforations further comprising opposite edge zones, opposite intermediate zones and a middle zone, wherein the bonded area of the opposite edge zones is less than the bonded area of the opposite intermediate zones and the bonded area of the opposite intermediate zones is less than the bonded area of the middle zone.
 2. The rolled tissue product of claim 1 wherein the opposite edge zones are disposed immediately adjacent to the opposite intermediate zones and the middle zone is disposed immediately adjacent to the opposite intermediate zones.
 3. The rolled tissue product of claim 1 wherein the opposite edge zones have a theoretical detach strength of 2200 gf or less, the intermediate zones have a theoretical detach strength from about from 2200 gf to about 2400 gf and the middle zone has a theoretical detach strength of about 2500 gf or more.
 4. The rolled tissue product of claim 1 wherein the opposite edge zones have a bonded area of about 20% or less, the intermediate zones have a bonded area from about 21% to about 23% and the middle zone has a bonded area from about 24% to about 26%
 5. The rolled tissue product of claim 1 wherein the length of the middle portion is at least about 40% of the sheet width (w).
 6. The rolled tissue product of claim 1 wherein the length of each of the opposite edge zones is from about 5% to about 20% of the length of the middle zone.
 7. The rolled tissue product of claim 1 wherein there is an increase in the theoretical detach strength from the edge zone to the middle zone and wherein the increase in theoretical detach strength is substantially linear.
 8. The rolled tissue product of claim 1 having a detach strength from about 1800 gf to about 3000 gf.
 9. The rolled tissue product of claim 1 having a geometric mean tensile strength from about 2000 g/3″ to about 3000 g/3″.
 10. The rolled tissue product of claim 1 having a CD tensile strength from about 2200 g/3″ to about 2500 g/3″ and a normalized detach strength of about 1.5 or less.
 11. The rolled tissue product of claim 1 wherein the bonded areas have a bond length ranging from about 0.50 mm to about 0.90 mm.
 12. The rolled tissue product of claim 11 wherein the bond length of the bonded areas is substantially equally in each of the zones.
 13. The rolled tissue product of claim 1 wherein the tissue web comprises a single-ply uncreped through air dried tissue web.
 14. The rolled tissue product of claim 1 having a CD tensile strength from about 2000 g/3″ to about 2500 g/3″ and a normalized detach strength of about 1.5 or less.
 15. A rolled tissue product comprising a tissue web spirally wound about a core and configured for peripheral dispensing, the tissue web comprising a plurality of spaced apart transverse lines of peroration that define individual tissue sheets therebetween, each sheet having a sheet length (l) and sheet width (w), each of the lines of perforations further comprising varying bonded areas that define opposite edge zones having a bonded area from about 20% to about 21%, opposite intermediate zones having a bonded area from about 22% to about 23% and a middle zone having a bonded area from about 24% to about 25%.
 16. The rolled tissue product of claim 15 wherein the opposite edge zones have a theoretical detach strength of 2200 gf or less, the intermediate zones have a theoretical detach strength from about from 2200 gf to about 2400 gf and the middle zone has a theoretical detach strength of about 2500 gf or more.
 17. The rolled tissue product of claim 15 wherein the length of the middle portion is at least about 40% of the sheet width (w).
 18. The rolled tissue product of claim 15 wherein the length of each of the opposite edge zones is from about 5% to about 20% of the length of the middle zone.
 19. The rolled tissue product of claim 15 wherein there is an increase in the theoretical detach strength from the edge zone to the middle zone is substantially linear.
 20. The rolled tissue product of claim 15 having a geometric mean tensile strength from about 2000 g/3″ to about 3000 g/3″ and a detach strength from about 1800 gf to about 3000 gf. 